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Chap 2

Chap 2. System Structures. Operating System Services. One set of operating-system services provides functions that are helpful to the user: User interface Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch Program execution I/O operations File-system

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Chap 2

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  1. Chap 2 System Structures

  2. Operating System Services • One set of operating-system services provides functions that are helpful to the user: • User interface • Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch • Program execution • I/O operations • File-system • Communications – Processes may exchange information, on the same computer or between computers over a network • Error detection

  3. Operating System Services (Cont.) • Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing • Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them • Accounting - To keep track of which users use how much and what kinds of computer resources • Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other

  4. User Operating System Interface • Command interpreter • allows direct command entry • Sometimes implemented in kernel, sometimes by systems program • Sometimes multiple flavors implemented – shells • Primarily fetches a command from user and executes it • Graphical user interface • User-friendly desktop metaphor interface • Many systems now include both CLI and GUI interfaces

  5. System Calls • Programming interface to the services provided by the OS • Mostly accessed by programs via a high-level Application Program Interface (API) rather than direct system call use • Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

  6. Example of System Calls • System call sequence to copy the contents of one file to another file

  7. Example of Standard API • Consider the ReadFile() function in the • Win32 API—a function for reading from a file

  8. System Call Implementation • Typically, a number associated with each system call • System-call interface maintains a table indexed according to these numbers • The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values • The caller need know nothing about how the system call is implemented • Just needs to obey API and understand what OS will do as a result call

  9. API – System Call – OS Relationship

  10. Standard C Library Example • C program invoking printf() library call, which calls write() system call

  11. System Call Parameter Passing • Three general methods used to pass parameters to the OS • Simplest: pass the parameters in registers • Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register • This approach taken by Linux and Solaris • Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system • Block and stack methods do not limit the number or length of parameters being passed

  12. Parameter Passing via Table

  13. Types of System Calls • Process control • end, abort • load, execute • create process, terminate process • get process attributes，set process attributes • wait for time • wait event, signal event • allocate and free memory • File management • create file, delete file, open,Close • read, write, reposition • get file attributes, set file attributes

  14. Types of System Calls • Device management • request device, release device • read, write, reposition • get device attributes, set device attributes • logically attach or detach devices • Information maintenance • Communications may be via shared memory or through message passing (using mailbox) • get time or date, set time or date • get system data, set system data • get process, file, or device attributes • set process, file, or device attributes

  15. Types of System Calls • Communications • create, delete communication connection • send, receive messages • transfer status information • attach or detach remote devices

  16. System Programs • System programs provide a convenient environment for program development and execution. The can be divided into: • File manipulation • Status information • File modification • Programming language support • Program loading and execution • Communications • Application programs

  17. Operating System Structure • MS-DOS – written to provide the most functionality in the least space

  18. Operating System Structure • Layered Approach • The operating system is divided into a number of layers (levels). The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. • With modularity, layers are selected such that each uses functions and services of only lower-level layers

  19. Operating System Structure • UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts • Systems programs • The kernel • Consists of everything below the system-call interface and above the physical hardware • Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level

  20. Operating System Structure • UNIX System Structure

  21. Operating System Structure • Solaris Modular Approach

  22. Virtual Machines • A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware • A virtual machine provides an interface identical to the underlying bare hardware • The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory

  23. Virtual Machines (Cont.) • The resources of the physical computer are shared to create the virtual machines • CPU scheduling can create the appearance that users have their own processor • Spooling and a file system can provide virtual card readers and virtual line printers • A normal user time-sharing terminal serves as the virtual machine operator’s console

  24. Virtual Machines (Cont.) (a) Nonvirtual machine (b) virtual machine

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